Postby carneyf1d » November 12th, 2009, 6:02 pm
Airfoils are quite complicated. The reason airfoils provide lift actually comes from viscous effects of air. A circulation of air is created around an airfoil and as a result, the lower surface of an airfoil has a lower velocity, and the upper surface has an increase in velocity. Bernoulli's equation relates velocity, density, and pressure. 1/2 * density * velocity ^2 + pressure = constant along the airfoil. Therefore when velocity increases, pressure decreases and vice versa. Since there is a pressure differential, the wing will lift.
Airfoils without camber, also called symmetrical, have a lift coefficient related to 2* pi * angle of attack. Angle of attack is in radians, or (degrees * pi / 180). Although at angles of attack greater than 10 degrees, the wing undergoes stall, where there becomes a separation of airflow, leading to a lot of drag and little lift (aka stalling out.)
Cambered airfoils on the other hand have a special property of having a negative angle of attack when there is zero lift. So if you have a cambered airfoil at -1 degree, youll get 0 lift, where as symmetrical airfoils all have 0 degrees angle of attack as zero lift. This zero lift angle is known as alpha_L=0 . The lifting coefficient of a cambered airfoil is 2* pi * (alpha - alpha_L=0).
Thus cambered airfoils will have higher lifting coefficients than symmetrical airfoils at the same angles of attack, making cambered foils better for this competition.
As to whether you should use simplex airfoils or your own design of camber is undetermined. Ill get back to you guys later with that info.
On a side note, this only briefly touches the subject of airfoil theory. If you really wanna find more, visit your local library. In addition, make sure the overall angle of attack takes into account wing aspect ratio and geometric design of the wing (elliptical or square).
good luck